This invention relates to a method of agglomerating carbonaceous material such as coal for use as fuel and to the fuel agglomerates made by this method. In particular, the invention relates to the use of an extract from coal or other materials of botanical origin as a binder for the fuel agglomerates.
There has been a long-felt need for a suitable inexpensive binder to consolidate the various coal and coal-related materials into weather-resistant agglomerates of convenient size for fuel use. Modern coal mining and coal cleaning techniques are generating increasing quantities of degraded coal materials. Coal preparation plants produce large quantities of fine size clean coal and refuse with high water or moisture content. The further use of such materials involves serious handling problems. Wet material can freeze in winter to form large masses that must be thawed or broken before handling and refuse fines are a significant environmental problem. With fine dry material, heavy dust losses and air contamination result, in addition to an unwarranted waste of an energy resource.
More stringent power plant emission standards and the increased interest in the use of coal slurries may result in an even greater amount of coal fine production in the future. Finer grinding may be required to liberate undesirable ash and sulfur impurities from coal prior to beneficiation and final utilization.
A parallel set of problems arise with low-rank coals such as lignite. Vast lignite deposits, often low in sulfur content, can be easily and inexpensively mined. Unfortunately, the use of lignite has been restricted generally to the immediate area of the deposits because of its high inherent moisture content and resultant lower Btu content. Its tendencies to degrade in particle size during handling and to spontaneous combust further restrict its use.
For more than half a century, these problems have been addressed, with attempts to provide fuel particles of convenient size and stable structure. For example, U.S. Pat. Nos. 1,452,992 (1923) and 1,790,356 (1929) disclose briquetting processes with asphalt, tar, pitch, etc. as binder to effect consolidating of fine coals or petroleum derived materials.
In more recent efforts, lignite pellets have been formed with asphalt emulsion or other emulsified binder materials. These processes are illustrated in U.S. Pat. Nos. 4,302,209 and 4,412,840, awarded to Baker et al and Goksel respectively. Although satisfactory pellets are formed, the cost of providing and applying the asphalt emulsion offsets the economic value of the process.
Therefore, it is an object of the present invention to provide an economic process for agglomerating particulate carbonaceous fuel.
It is a further object to provide a method for agglomerating coal particulates which uses an inexpensive coal extract as binder material.
It is also an object to provide a process for producing fuel agglomerates of convenient size with good stability to permit handling and exposure to weather during the course of fuel distribution.
It is a further object to provide a weather resistent fuel agglomerate of good mechanical properties.
In accordance with the present invention, there is provided a method of producing weather resistent carbonaceous agglomerates suitable for fuel use. A carbonaceous material that includes chemically combined oxygen as humic acid or humate salt is treated with an aqueous alkali solution to extract humates and thereby provide a binder liquid. A particulate carbonaceous fuel with a substantially greater heating value than the humic acid containing material is blended with the binder liquid to permeate the humate solute into the fuel particulates. The particulates, as thus treated with binder, are formed into agglomerates and dried to reduce moisture content and convert the humate solute to a water-resistent binder material.
In more specific aspects of the invention, the humic acid containing carbonaceous material is formed by the mild oxidation of a coal-derived material such as leonardite, peat, soil or decayed botanical residue. The carbonaceous material includes carbon and oxygen on a weight ratio of no more than six to one on a moisture-free basis.
In further more specific aspects, the humates are extracted from the oxidized carbonaceous material into an aqueous alkali solution selected from solutions of alkali metal hydroxides, alkali metal carbonates, or ammonia.
In other aspects, the agglomerates are dried in air at a temperature of about 100.degree.-200.degree. C. sufficient to reduce moisture content to less than 15% by weight and solidify the humates into a binder permeated into the fuel particulates throughout the agglomerates.
In yet other aspects of the invention, a weather resistant fuel agglomerate of suitable size, shape and mechanical strength for conveyance and handling is provided. The agglomerate includes carbonaceous fuel particles bound together by a humate constituent permeated into and combined with surface portions of the carbonaceous particles making up the agglomerate. In more specific aspects, the agglomerate comprises by weight about 60-90% coal particles, 0-25% moisture and 1-10% humate constituent.